Conventional GaN high voltage Schottky diodes can be classified into two main categories: lateral devices and vertical devices. Lateral GaN Schottky diodes make use of a 2DEG (two dimensional electron gas) inherently provided by a conventional AlGaN/GaN system and require a minimum lateral distance between the anode and cathode contacts to sustain a high voltage. Vertical GaN Schottky diodes typically make use of a GaN buffer and do not require the presence of a lateral 2DEG channel. Instead, the anode is formed on the top a lightly doped GaN buffer and the cathode is represented by a lower contact disposed at the bottom of the GaN buffer. In order to have a good bottom contact, a highly doped layer is needed between the bottom contact and the GaN buffer.
The presence of a high mobility 2DEG in lateral diode devices achieves high current compared to their vertical counterparts. However vertical diode devices have better area efficiency due to the current flow direction and therefore have considerably reduced device dimensions as compared to lateral devices. Moreover, a Schottky contact directly placed on top of a GaN buffer results in a lower forward bias when compared with an AlGaN/GaN system. It therefore would be desirable to have a GaN device possessing the high current advantage of conventional lateral GaN devices and the area efficiency and low forward bias of conventional vertical GaN devices.